The invention relates to fabricating three-dimensional annular fiber structures.
A particular field of the invention is fabricating thick annular fiber preforms for constituting the fiber reinforcement of annular parts made of composite material, in particular brake disks, such as disks made of carbon/carbon (C/C) material for airplane brakes.
One usual process for making annular fiber preforms consists in superposing and bonding together two-dimensional plies to build up plates from which the preforms are cut out. Such a process, as described for example in U.S. Pat. Nos. 4,790,052 and 5,792,715, presents the manifest drawback of wasting a large amount of material, which drawback is particularly penalizing when the fibers are relatively expensive, as is the case for carbon fibers or carbon precursor fibers.
Various proposals have been made to avoid that drawback and to obtain a fiber structure directly in a shape that is as close as possible to the desired annular shape. Thus, proposals are made in U.S. Pat. Nos. 6,009,604 and 5,662,855 to make preforms by superposing and bonding together layers formed by braids that have been wound flat to form a helix. U.S. Pat. Nos. 6,363,593 and 6,367,130 propose using a helical cloth wound in superposed turns that are bonded together.
Those techniques require a fiber fabric (braid or helical cloth) to be made that is an intermediate product between the yarns or tows of fiber and the annular preform that is to be made.
In order to avoid that intermediate step, patent document WO 98/49382 proposes forming a disordered mass of fibers on an annular support and bonding the fibers together by needling. Nevertheless, that document is silent about the means that need to be used in practice in order to obtain an annular preform that is satisfactory, at least in terms of uniformity, for use in certain applications where requirements concerning uniformity are very high, as are requirements concerning quality control of mechanical properties, as applies in particular when the preform is for use as an airplane brake disk preform.
US patent document 2005/0172465 proposes forming an annular preform by regular and controlled deposition of short fibers on a rotary annular turntable with progressive needling. It is thus possible to obtain a preform that is uniform, but at the cost of passing via an intermediate step of obtaining short fibers.